Powdered iron magnetic core materials



Feb. 26, 1957 e. KATZ 2,783,208

POWDERED IRON MAGNETIC CORE MATERIALS Ffgled Jan; 4, 1954 QEAMS 2, 7ISO-PEOPYL NAPHTHALENE SOD/UM SUI. FONATE PER I00 GRAMS POM DEEINVENTOR.

, George [(322 ATTORNEY 'POWDERED IRON MAGNETIC CORE MATERIALS ljnitedStates Patent George Kat'z,.'Philadelphia,,- Pa., assignor to RadioCorporation of America, a corporation of Delaware Application January 4,1954; Serial No. 401,767 7 Claims. or. 252-625 This inventionrelates tomagnetic. cores and more particularly to improved magnetic cores formedof compressed powderediron.

Magnetic cores made of compressed powdered iron, the individualparticles of which are insulated from each other and bound together byresinous materials are well known. They are generally suitable for useas induction cores to operate at relatively high electrical frequencies.One method of making such cores comprises mixing. powdered iron with adilute solution of a polybasic inorganic acid such as sulfuric orphosphoric acid. The iron is preferably, although not necessarily,prepared by the carbonyl process which produces relatively pure iron inthe form of relatively small particles which may run about 3/L-1QLL insize. In many instances it is important that the iron particles be of asmall size since eddy current losses in a compressed core decrease asthe particle size decreases.

Treating the powder with polybasic acid produces an insulating coatingupon the individual iron particles. The powder is then mixed with abinder such as a phenol formaldehyde resin and molded into a desiredshaped body.

One object of the instant invention is to provide an improved magneticcore.

Another objectis to provide a compressed powdered i on magnetic corehaving improved electrical loss characteristics.

Another object isto provide a powdered iron magnetic core havingimproved physical strength and able to withstand relatively high stress.

Another object is to provide magnetic core bodies comprising powderediron and having both improved strength and improved electrical losscharacteristics.

These and other objects may be accomplished by the practice of theinstant invention which provides an improved magnetic core body. It hasnow been discovered that improved core bodies may be produced bytreating powdered iron with a polybasic acid solution that includes arelatively small proportion of a sulfonated derivative of naphthalene.The treated powder .is molded according to previous practice to formcore bodies of improved strength and having improved electricalproperties.

The invention will be described in greater detail in connection with thedrawing of which:

The single figure is a chart illustrating the improvement in propertiesprovided by the practice of the instant invention.

*According to a preferred embodiment of the instant invention a mass ofcarbonyl iron powder consisting essentially of iron particles about 3u.10,u. in their greatest dimensions is wet with a solvent such asacetone that does not react with iron. About 50-100 cc. of acetone areused for each 100 gm. of iron powder. For purposes of convenience thepresent example described the treatment of 100 gm. of powdered iron.Larger quantities ably mixed in a mill such as a Simpson mixer.

'lce

may be treated with correspondingly larger quantities of the othermaterials involved.

A second mixture is prepared by dispersing about .02 gm. of 2,7iso-propyl naphthalene sodium sulfonate in about 50-100 cc. of the samesolvent used to wet the iron, conveniently, acetone. About 1-5 gm. ofgranodine is added to the acetone-sulfonate solution. Granodine is atrade name for an aqueous 40% phosphoric acid solution that includesabout 6%-12% by weight zinc phosphate.

The acetone-sulfonate-granodine mixture is added to the powdered ironand thoroughly mixed therewith. The mixture is continuously stirred and,preferably, is heated to a temperature of about 40-50 C. to drive oifsubstantially all the acetone and water. For small batches the mixingmay be done in any convenient vessel such as a laboratory beaker. Largerquantities are prefer- This treatment fnrms an insulating coating on theindividual particles of the iron powder and prepares them for molding'with a resin. i

Any of a large number of phenol formaldehyde resins is satisfactory formolding core bodies according to the invention. A preferred resin is onethat is known by the trade name of F-D-4-80M (manufactured by the AcmeResin Corporation, 1401 Circle Avenue, Forest Park, Illinois). Thisproduct comprises a solution of about 60% phenol formaldehyde resin and40% volatile solvent such as methyl alcohol. About 5 gm. of the resinsolution is. diluted with about 50-100 cc. of acetone. The treated ironpowder is wet down with about 50-100 cc. of acetone and the dilutedresin solution is added to the Wet powder. The mixture is stirredcontinuously and gently heated to mix the resin and the iron powderintimately together and to drive oil the acetone and moisture. Thismixing may be conveniently carried out in a Simpson mixer or other millto produce pellets of about 18-20 mesh average size.

A molding lubricant consisting of about gm. of powdered zinc stearate orstearic acid is coated on the pellets by tumbling them in a barrel withthe wax.

The pellets are then molded at about 50,000 lbs. per square inchpressure into bodies of a desired shape. The bodies are heated at about145 -155 C. for /2 hour or more to cure the resin.

An essential feature of the invention is the inclusion ot a sulfonatedderivative of naphthalene in the granodine solution utilized in theinitial treatment of the iron powder. The naphthalene derivative ispreferably included in the granodine in the proportions of about .01-.08gm. per gm. of iron powder to be treated. The other steps heretoforedescribed are not critical in the practice of the invention but may bevaried within the general limits customary in the art. For example,powdered iron produced by processes other than the carbonyl process maybe utilized and the particle size of the iron is not critical. Also,other polybasic inorganic acids such as sulfuric acid may be utilized inplace of phosphoric acid. t is generally important, however, that theiron powder be relatively clean and free from grease and other organicmatter.

Improved but somewhat less satisfactory results may be produced bysubstituting other sulfonated naphthalene derivatives in place of theiso-propyl naphthalene sodium sulfonate heretofore described. Forexample, and 18% improvement in transverse strength may be provided in acore body when utilizing the sodium salt of naphthalene- 2,7 disulfonicacid in the proportion of about .04 gm. per 100 gm. iron powder. About a10% improvement in strength is provided by Z-naphthalene sulfonic acidwhen utilized according to the invention in the proportions of about .01gm. per 100 gm. iron powder. As may be seen from curve B of the figure,however, a 38% improvement in transverse strength is provided by the useof 2,7 iso-propyl naphthalene sodium sulfonate as described heretoforein connection with the preferred embodiment.

It should also be noted that the practice of the instant inventionprovides a significant improvement in the electrical losscharacteristics of a magnetic core. As may be seen from curve A of thedrawing, Q, an arbitrary inverse measure of electrical losses in a corebody measured at 1 megacycle per second is improved about 4% by thepractice of the preferred embodiment as described heretofore.

There have thus been described improved magnetic core bodies comprisingpowdered iron and a resin binder and also including relatively smallproportions of a sulfonated naphthalene derivative. These bodies haveimproved strength and smaller electrical losses compared to previousbodies made in an exactly similar manner but without the sulfonatednaphthalene derivative.

What is claimed is:

1. A method of making a compressed magnetic core body comprising thesteps of wetting a mass of iron powder with a mixture comprising anaqueous solution of phosphoric acid and zinc phosphateand a substanceselected from the group consisting of 2,7 iso-propylnaphthalene sodiumsulfonate, the sodium salt of naphthalene 2,7 disulfonic acid, andZ-naphthalene sulfonic acid thereby, said substance being present in theproportions of about .01 to .08 gm. and said zinc phosphate beingpresent in the proportion of about .06 to .60 gm. per 100 gms. of ironpowder, to form an insulating coating upon the individual particles ofsaid powder, drying said powder and molding said dried powder with aphenol formaldehyde resin binder to form a core body;

2. The method according to claim 1 in which said solution comprises 40%aqueous phosphoric acid and 6% to 12% by weight ofzinc phosphate inacetone.

3. The method according to claim 2 in which said substance selected fromsaid group is 2,7 iso-propyl naphthalene sodium sulfonate.

4. A product prepared according to the process of claim 1 wherein saidsubstance is a sodium salt of naphthalene 2,7 disulfonic acid.

5. A product prepared according to the process of claim 1 wherein saidsubstance is 2-naphthalene sulfonic acid.

6. A product prepared according to the process of claim 1 wherein saidsubstance is 2,7 iso-propyl naphthalene sodium sulfonate.

7. The product of claim 6 wherein said 2,7 iso-propyl naphthalene sodiumsu-lfonate is present in proportions of about .02 gm. per gms. of ironpowder.

References Cited in the file of this patent UNITED STATES PATENTS2,106,882 Betz Feb. 1, 1938 2,227,945 Neilson Jan. 7, 1941 2,306,198Verweij et al. Dec. 22, 1942 2,601,212 Polydorofl. June 17, 1952 FOREIGNPATENTS 403,373 Great Britain Dec. 15, 1933 523,864 Great Britain July24, 1940 OTHER REFERENCES Derksen, A. P. C. Spec. Serial No. 400,859,published April 27, 1943, 18-55M.

1. A METHOD OF MAKING A COMPRESSED MAGNETIC CORE BODY COMPRISING THESTEPS OF WETTING A MASS OF IRON POWDER WITH A MIXTURE COMPRISING ANAQUEOUS SOLUTION OF PHOSPHORIC ACID AND ZINC PHOSPHATE AND A SUBSTANCESELECTED FROM THE GROUP CONSISTING OF 2,7 IDO-PROPYL NAPHTHALENE SODIUMSULFONATE, THE SODIUM SALT OF NAPHTHALENE 2,7 DISULFONIC ACID, AND2-NAPTHALENE SULFONIC ACID THEREBY, SAID SUBSTANCE BEING PRESENT IN THEPROPORTIONS OF ABOUT .01 TO .08 GM. AND SAID ZINC PHOSPHATE BEINGPRESENT IN THE PROPORTION OF ABOUT .06 TO .60 GM. PER 100 GMS. OF IRONPOWDER, TO FORM AN INSULATING COATING UPON THE INDIVIDUAL PARTICLES OFSAID POWDER, DRYING SAID POWDER AND MOLDING SAID DRIED POWDER WITH APHENOL FORMALDEHYDE RESIN BINDER TO FORM A CORE BODY.